1. Field of the Invention
This invention relates to the allocation of radio frequency channel resources in a partitioned wireless telecommunications system. More particularly, the invention concerns a method for use in a cellular telephone system, personal communications service (PCS) network, or equivalent enterprise for efficiently performing flexible channel allocation to support call origination, termination and handoff.
2. Description of the Prior Art
Modern wireless telecommunications systems employ the concept of a partitioned service area formed by a network of contiguous geographic subdivisions, known as cells. Each cell is served by a base station that communicates with mobile units within the cell via assigned radio frequencies. The base station provides a link between the mobile units and a land-based communications network, such as a public switched telephone network, to which the base station is connected via a Digital Cellular Switch (DCS). Each base station handles call origination and termination requests from mobile units within a cell, and performs the important function of negotiating call handoffs with other base stations on behalf of mobile units transitioning between cells. A computerized Mobile Switching Center (MSC) assists the base stations to perform these functions.
One of the implications of a partitioned wireless telecommunications system is that radio frequency channels may be reused, but this is only true for cells that are relatively remote from each other. Base stations that are three cells apart or less are considered to be potentially mutually interfering and will not be allowed to share channels without restriction. Using the conventional hexagonal cell model, any given cell has thirty-six first, second and third tier cell neighbors that are potential interferers. Considering that each cell may be subdivided into six sectors serviced by individual directional antennas, each sector has seventy-two potentially interfering sector neighbors. For these potentially interfering cells and cell-sectors, available channels must be carefully allocated in a manner that avoids substantial inter-cell or inter-sector interference.
Although channels can be allocated between potentially interfering cells and sectors in mutually exclusive fashion, such that simultaneous channel sharing never occurs, this is inefficient because channels tend to be underutilized. It would be preferable to allocate channels using a flexible channel allocation technique that allows channel sharing under appropriate conditions, yet does not consume excessive processor resources at the computerized mobile switching center. What is required is a system for efficient flexible channel allocation that minimizes processor overhead and system latency, and provides robust service to end users at call setup and handoff time.